AND ITS INHABITANTS 25 



regarded as very important and he believes this diffused 

 matter contributed much of the earth substance, very slowly 

 and in a dust-like form. This is one of the critical points 

 in the details of the theory upon which turns much of the 

 development of his following argument. 



Chamberlin conceives the earth to have been built up as 

 a solid body, not to have been fluid or viscous at any time 

 later than the early nuclear stage and to have begun to 

 hold an ocean by the time it contained 30 or 40 per cent 

 of the present mass. Such liquid rock as was generated 

 by compression or radioactivity during earth-growth is re- 

 garded as having been kneaded and squeezed to the surface, 

 where it solidified approximately as fast as it was formed. 

 In earth-growth, the denser planetesimal dust, he argues, 

 tended to be somewhat segregated into the primitive ocean 

 basins and served to maintain in them, as the earth was 

 built outward, a greater density than in the elevated zones 

 between, establishing thus a relation between density and 

 elevation. 



It seems a debatable question if such a large proportion 

 of the added material was necessarily dust-like and capable 

 of being weathered, sorted, and distributed by the primitive 

 atmosphere and ocean. In fact, from this beginning of 

 earth-growth the preponderance of the evidence appears to 

 the writer to be against those sub-hypotheses which Cham- 

 berlin has followed. This evidence, its bearings and con- 

 clusions, will form the following parts of this article. It will 

 be of ultimate value to both lines of argument that each may 

 be weighed against the other. 



HYPOTHESIS OF EARTH-GROWTH BY RAPID INFALL OF 



PLANETOIDS 



Preliminary statement. Alternative views quite different 

 from those which have been presented under the previous 



